1. Field of the Invention
The present invention relates to substrate processing methods, manufacturing method of photomasks, photomasks, and device manufacturing methods, and more particularly to a substrate processing method that includes a patterning step in which patterning of a resist on a substrate is performed by exposure for manufacturing electronic devices (microdevices) such as a semiconductor, a manufacturing method of a photomask used in the patterning step, a photomask manufactured by the manufacturing method, and a device manufacturing method that uses the substrate processing method or the photomask.
2. Description of the Background Art
When manufacturing electronic devices, in the substrate processing step or the wiring step in a wafer processing step (pre-process), a series of processing such as a patterning step (i.e. exposure step) in which patterning of a resist layer formed on a wafer is performed by exposure, a development step in which the wafer that has been patterned is developed, an etching step in which the wafer (or a film on the wafer) is etched (mainly dry etching) with the resist pattern (resist image) that has been developed serving as a mask and the like is repeatedly performed.
However, recently, it was discovered that in some cases the size of the pattern formed after etching differs from the size of the pattern in target after etching even if the resist image of the same size as the target is formed by patterning. It turned out that especially in the case when an isolated pattern and a dense pattern that are supposed to have the same resist image linewidth are formed on the same photomask, the tendency was high of the linewidth after etching varying per each pattern. In the case an isolated pattern and a dense pattern are formed on the same photomask, the linewidth of each of the patterns on the photomask is normally set taking into consideration the optical proximity effect.
As an example of using a space pattern, the wiring step will be described. In the wiring step, as the wiring material, aluminum (Al) has been conventionally used. In recent years, however, copper (Cu), which has a lower electric resistance than aluminum and is suitable for finer patterning and high-speed operations, has become to be used. However, with copper, a technique referred to as the damascene method is employed as the technique for forming wiring without etching the copper (refer to, for example, Kokai (Japanese Patent Unexamined Application Publication) No. 2002-270586), taking into consideration the fact that etching rate control is difficult when compared with aluminum. In the copper wiring by the damascene method, wiring is formed by depositing copper by plating or the like after forming a groove in an interlayer insulating film, and removing the copper on the surface by CMP (Chemical Mechanical Polishing).
When a space pattern is used as the pattern of the photomask as in the case when the damascene method is employed, it has recently been discovered that even if a resist image of the same size as the target size is formed by patterning, the tendency was high of the size of the pattern formed after etching being different from the pattern size in target after etching.
Meanwhile, in electronic devices such as a semiconductor device, due to the progress in finer geometry, higher precision in processing size is required at a nanometer level. Because unevenness or variation in the finished dimension of devices particularly affects the yield or the operation speed of the device, requirements to reduce unevenness and variation are pressing.
According to such a background, expectations were high for a technology that allows the pattern size after etching to be set for certain at a desired value.
In order to investigate the cause of the phenomenon in which the pattern linewidth after etching differs from the pattern linewidth in target, the inventor performed various experiments (including simulation). As a consequence, the inventor reached an assumption that the main cause for the relation between the linewidth of the resist image after development and the linewidth of the pattern after etching varying was due to the profile of the resist image differing, for example, depending on exposure conditions of the pattern or the like.
Further details on this point will be described, using a space pattern as an example. In the space patterns after development illustrated in the upper section of FIGS. 6A and 6B, the resist images both have the same linewidth (the linewidth at the bottom of the resist image) WDb, however, between linewidths WDt1 and WDt2 close to the top of the resist images, a relation WDt1<WDt2 exists, which shows an obvious difference in the resist profiles of the space patterns. Because of such difference in the profiles, deformation condition of the resist image profiles after cure (heat treatment) illustrated in the middle section of FIGS. 6A and 6B greatly differs. More specifically, the resist image in FIG. 6A that has a good profile greatly collapses (deforms) due to the heating (other than heat treatment using heaters or the like, heat treatment by ultraviolet light irradiation or the like is also included) in the cure process when compared with the resist image in FIG. 6B that has a bad profile. As a consequence, in the resist image after cure, the linewidth of the resist image is narrower in FIG. 6A than in FIG. 6B (WDb1<WDb2). Accordingly, the linewidth of the space patterns after etching illustrated in the lower section of FIGS. 6A and 6B, FIG. 6A is narrower in FIG. 6A when compared with FIG. 6B.
In order to obtain a resist image of the same linewidth in an isolated space pattern and a dense space pattern, the linewidth of the isolated space pattern on the photomask is set wider than the linewidth of the dense space pattern, taking into consideration the optical proximity effect. Accordingly, in the case exposure is performed under the same exposure conditions, the linewidth of the resist image of the isolated space pattern and the resist image of the dense space pattern is substantially the same, however, the profiles of the resist images usually differ, and as a consequence, the linewidth after etching varies in each space pattern.
On further investigation, the inventor consequently found out that there was a close relation between the resist image profile and the projected image (the aerial image) of the pattern. More specifically, in the upper half of FIGS. 7A and 7B, a resist image of a space pattern that has a good profile and a resist image of a space pattern that has a bad profile are illustrated. Further, in the lower half of FIGS. 7A and 7B, aerial images (projected images) of the pattern corresponding to each of the resist images in the upper half are illustrated. As is obvious from FIGS. 7A and 7B, in both cases when the profile of the resist image is good and when the resist image profile is bad, the target linewidth (Target CD) of the resist image of the space pattern is set by linewidth WDb at the bottom of the resist image, and the bottom linewidth WDb coincides with the distance WDb (hereinafter referred to as “projected image linewidth”) between two intersecting points of the projected image of the corresponding pattern and a predetermined slice level SL. Further, linewidths WDt1 and WDt2 (>WDt1) in the vicinity of the top of each of the resist images coincide with a slice levels SL′, which is a slice level that is lower by a predetermined value than the above-mentioned predetermined slice level SL of the projected image of the corresponding pattern.
Further, as is obvious when comparing FIGS. 7A and 7B, the change in the projected image linewidth with respect to the change in the slice level is smaller in the sharp-edged projected image shown in FIG. 7A (corresponding to the resist image that has a good profile) than the rounded-edged projected image shown in FIG. 7B (corresponding to the resist image that has a bad profile).
From the description above, the inventor reached a conclusion that there was a close relation between the sharp-edged feature of the projected image of the pattern and the profile of the resist image, or as a consequence, the device linewidth characteristics that has a close relation with the profile (related to the linewidth of the pattern after cure (or etching)).